If exposed to light, beer is known to develop a "light struck" or "skunky" flavor. This is due to the light sensitivity of the conventional hop bittering substances which make up an essential ingredient of beer. The invention disclosed here relates to the production of tetrahydro-iso-.alpha.-acids. Tetrahydro-iso-.alpha.-acids are well-known as bittering agents derived from hops. However, they are insensitive to light and may be used to brew beer that will not subsequently develop a skunky flavor. Before the invention claimed here is described and explained, it will be helpful to first provide a brief history of hop usage in the brewing industry.